In recent years, new technologies for electrical power generation excellent in energy efficiency and environmental properties have drawn attention. Among these technologies, a solid polymer fuel cell having a polymer solid electrolyte membrane has characteristics such that energy density is large, and start and stop are easy since a driving temperature is low as compared with fuel cells in other modes, and thus, development of the solid polymer fuel cell has been progressed as a power supply for an electrical automobile and dispersed power generation.
A proton conductive ion exchange membrane is generally used for a polymer solid electrolyte membrane. It is required that the polymer solid electrolyte membrane has characteristics such as mechanical strength and fuel permeation suppressing property for preventing permeation of hydrogen, etc that is a fuel in addition to proton conductivity. It has been found that irregularity in thickness, wrinkles and unevenness of an electrolyte membrane have an influence on these characteristics.
Conventionally, a method of drying by applying tension to a membrane has been reported as a means for overcoming wrinkles and unevenness (for example, please see Japanese Patent Application Laid-Open (JP-A) No. 2003-192805). However, there was a problem such that a thickness becomes nonuniform between a fixed part periphery and a part separated furthest from the fixed part. Further, there was also a problem such that fixing only during drying cannot sufficiently overcome wrinkles and unevenness generated in steps before drying. In particular, as to a polymer solid electrolyte membrane produced by, what is called, solution membrane formation (i.e. forming a membrane by casting a solvent solution of a polymer electrolyte on a support and then removing the solvent to form a membrane), not only improvement in stability of a membrane shape, but also improvement in stability of a membrane form, stability of membrane characteristics, and the like have been required.